The invention concerns an overload protection device comprising a housing which is designed to be mounted to a manipulation device, a tool holder for mounting a tool, which is movably disposed on the housing, a pretensioning unit designed for a pretensioning force between the housing and the tool holder, and a switching unit that switches in response to relative motion between the housing and the tool holder.
Overload protection devices are known in the art and are used in manipulation devices that are operated by external forces, such as e.g. axially or path-controlled industrial robots, in order to prevent damage caused by collisions through movement between the manipulation device and objects in the vicinity of the manipulation device. Towards this end, an overload protection device has a housing that can be mounted to the manipulation device, e.g. a receiving flange of a robot arm. A tool holder, e.g. in the form of a tool flange, is disposed on the housing and is designed to receive manipulation tools, e.g. gripping means, processing means and measuring means. The tool holder is thereby movably connected to the housing to permit relative motion between the housing and the tool holder, in particular, deflection of the tool holder. Linear and/or rotational relative motion may thereby be performed in dependence on an application range of the manipulation devices provided on the tool holder. The relative motion may be limited by the construction of the housing and the tool holder mounted thereto. In order to prevent undesired relative motion, a pre-tensioning means provides a pretensioning force between the housing and the tool holder such that relative motion only occurs when the pre-tensioning force has been overcome. In the event of a collision between the manipulation tool and an object, the collision force is thereby limited by the magnitude of the pre-tensioning force. Since one cannot exclude that an available motion tolerance of the relative motion between the housing and the tool holder is sufficient to completely accept the motion exercised by the manipulation device, a switching unit is provided between the housing and the tool holder which generates a switching signal in case of minimum deflection of the tool holder relative the housing, that can be passed on to a control means of the manipulation device in order to stop the motion of the manipulation device and optionally move it in the opposite direction.
One conventional embodiment of an overload protection device is the model OPS 80 of the Assignee, which is shown in current catalogues. The OPS 80 has a cylindrical housing with mounting bores for mounting to an industrial robot. The cylindrical housing also has a cylindrical tool holder that it is mounted such that it can be linearly displaced and rotated. The tool holder may be loaded with a pretensioning force via a pressure piston or a spring means, thereby permitting transmission of a constructively limited torque or a corresponding force that is required for using a tool mounted to the tool holder. Proximity switches are disposed at a front end of the housing facing the tool holder, which are separated from each other by 120° and which can trigger a switching signal in the event of a collision and the resulting approach of the tool holder towards the housing, thereby stopping the motion of the manipulation device. U.S. Pat. No. 4,717,003 discloses an overload protection device that has spring elements for generating a pre-tensioning force. The separation between the housing and a tool plate is thereby determined by sensors. When a predetermined separation is exceeded, a signal is issued.
DD 252 512 A3 discloses an adapter with collision protection having a basic housing. The basic housing has a pressurized volume that is sealed by a membrane. When a flange is lifted from the locking means, a sensor emits a signal.
It is the underlying purpose of the invention to provide an overload protection device of the above-mentioned type, which facilitates the construction thereof and improves its flexibility.